Climate change and extinction: one third of species could soon disappear

Since the end of the 19th century, Earth has warmed by about 1.3 degrees Celsius. This seemingly small change has already had profound effects on life on our planet. Some species have managed to adapt: birds have become smaller, lizards and insects have changed their colors, and many animals have expanded into new habitats. These adjustments help them survive in a changing environment.

But there are also many species that cannot adapt fast enough. Rising temperatures caused by climate change are leading to more fires in regions such as the Amazon and Australia, destroying animal populations. Rising sea levels are causing islands to disappear and wiping out the habitats of the animals living there. For example, the Bramble Cay melomys went extinct more than ten years ago due to sea-level rise.

The effects are also visible in the oceans. Higher temperatures reduce plankton production—an important food source for many marine fish. The Galápagos damselfish lost its livelihood as a result and went extinct. In Hawaii, climate change is bringing mosquitoes that transmit avian malaria to higher elevations, which had previously served as safe refuges for the remaining native bird species.

Amphibians are also heavily affected. The fungal disease chytridiomycosis, promoted by climate change, has already wiped out several species. Even plants are not spared: the Key Largo tree cactus, once native to the United States, has become locally extinct due to rising sea levels. These examples show that climate change threatens biodiversity worldwide in many ways—from altered living conditions to direct eradication.

Already 160,000 species threatened by climate change

Climate change has enormously increased the extinction risk for many animal and plant species. Mark C. Urban, director of the Center of Biological Risk at the University of Connecticut, investigated in a recent study, published in the journal Science, how great this threat actually is. To do so, he evaluated 131 studies that developed projections for the fate of numerous species—a so-called meta-analysis.

The focus was on biological mechanisms that influence how well species cope with changing conditions such as rising temperatures. These include, for example, their ability to colonize new habitats or their resilience to environmental change. Urban’s analysis shows which species are especially at risk and how those risks develop over time. These results are crucial for better understanding the effects of climate change on biodiversity and for planning targeted measures.

Projections for extinction

Already today, at warming of 1.3 degrees Celsius above preindustrial levels, about 1.6% of all known species are threatened with extinction—equivalent to around 160,000 species. But this is only the beginning. Urban’s models show how the risk develops as temperatures continue to rise:

• 1.3 °C (current warming): 1.6% of species threatened
• 1.5 °C (Paris Agreement target): 1.8%
• 2 °C (official Paris Agreement target): 2.7%
• 2.7 °C (current climate policy): 5%
• 4.3 °C (higher-emissions scenario): 14.9%
• 5.4 °C (worst-case scenario): 29.7%

Urban estimates that without consistent climate policy, up to 500,000 species could go extinct—half a million animals and plants would then be lost forever. Every species plays an important role in its ecosystem and often contributes to human well-being and health. Even small percentages represent massive losses that could endanger the balance of nature and ultimately our own foundations of life.

Particularly threatened habitats

The risk that species will go extinct due to climate change varies strongly by region. Australia and New Zealand show the highest risk at 15.7%, followed by South America at 12.8%. In Asia (5.5%) and the Arctic (3.8%), the risk is significantly lower, while North Africa is high at 17.4%. For the oceans, a moderate risk of 6.1% was estimated.

The high threat level in Australia and New Zealand is due to the fact that many species there are constrained in their ability to adapt by geographic barriers such as the sea. In South America, the loss of biodiversity hotspots threatens numerous species with small ranges and specialized habitats that offer no alternatives.

In the Arctic, many species benefit from their large ranges and can expand into new, warmer regions. But this does not protect the northernmost species, which depend on the vanishing sea ice. In the Southern Hemisphere, narrowing landmasses further limit the adaptive capacity of species. Even regions with lower average risk, such as Asia or the Arctic, still contain highly threatened species, showing that lower averages do not mean safety.

Not all species and ecosystems are equally affected

Urban’s study shows that the threat posed by climate change depends on a species’ taxonomic group and habitat. Within each group, however, individual species can still be especially vulnerable.

Amphibians have an above-average extinction risk of 10%. Their dependence on specific habitats such as freshwater makes them especially vulnerable. In addition, they are heavily threatened by weather extremes and diseases such as chytrid fungal infection, which is further promoted by climate change.

Birds are less threatened overall at 5.5%, since their mobility often allows them to colonize new habitats. Even so, highly threatened species also exist among them, especially on islands, where limited area and invasive species make adaptation more difficult. Broad generalizations should therefore be avoided, as the risks vary greatly from species to species.

The escalator to extinction

Most of these extinctions affected species in island, mountain, and freshwater ecosystems—areas already considered especially vulnerable. However, climate change usually played a supporting rather than exclusive role; traditional threats such as habitat loss and invasive species were often also decisive.

In mountains, where extinction risk is 14.8%, species quickly run into geographic limits. As temperatures rise, many species shift to higher elevations until they eventually reach the summit—and run out of space. Scientists refer to this phenomenon as the “escalator to extinction.”

Island species are also heavily affected, with a risk of 12%. Their small populations and limited land area make them especially vulnerable. Added to this are invasive species that further impair the already scarce habitat, as well as challenges such as rising sea levels, which are intensified by climate change.

Freshwater ecosystems are also highly threatened, with an extinction risk of 10.5%. The species living there suffer from pollution, water extraction, invasive species, and limited mobility. This combination makes them especially vulnerable to the rapid changes brought by climate change.

Climate protection as the key to preserving biodiversity

Urban’s study clearly shows that climate change significantly increases extinction risk. However, many unknown or rare species were not included, which suggests that the actual risks are probably even higher.

Even so, the results underscore the urgency of political measures to limit global warming. While nearly 30% of species could go extinct at warming of 5.4 degrees Celsius, a reduction to 4.5 degrees Celsius would lower this risk to 5%. Better still would be achieving the 1.5-degree target, which could keep the risk below 2%.

Urban makes clear that even the loss of 5% of species would have catastrophic consequences for ecosystems and for the people who depend on them. Especially at risk are amphibians as well as species in freshwater, island, and mountain regions, particularly in South America, Australia, and New Zealand.

The study provides a solid basis for prioritizing climate protection measures and developing targeted strategies to protect threatened species and regions. What matters is to contain climate change in order to avoid long-term damage to biodiversity. The report calls for halting species loss — not only in the interest of nature, but also for future generations that should benefit from a diverse environment.

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Source

• Mark C. Urban, Climate change extinctions. Science 386, 1123-1128 (2024). DOI: 10.1126/science.adp4461